Chimney: From Wikipedia: "A rock cleft with vertical sides mostly parallel, large enough to fit the climber's body into. To climb such a structure, the climber often uses his head, back and feet to apply opposite pressure on the vertical walls."

Steps

Squeeze: a horrible place you have to crawl through, and it's touching you

Crawl: like a squeeze but not as bad; the walls and ceiling aren't touching you all the time